Request test for Category

api_controller.rb

module Admin::V1
  class ApiController < ApplicationController
    include Authenticable

    def render_error(message: nil, fields: nil, status: :unprocessable_entity)
      errors = {}
      errors['fields'] = fields if fields.present?
      errors['message'] = message if message.present?

      render json: { errors: errors }, status: status
    end
  end
end

categories_controller.rb

module Admin::V1
  class CategoriesController < ApiController
    def index
      @categories = Category.all
    end

    def create
      @category = Category.new(category_params)
      save_category!
    end

    private

    class ApiError < StandardError; end

    def category_params
      return {} unless params.key?(:category)

      params.require(:category).permit(:id, :name)
    end

    def save_category!
      @category.save!
      render :show
    rescue ApiError
      render_error(fields: @category.errors.messages)
    end
  end
end

categories_request_spec.rb

require 'rails_helper'

RSpec.describe "Admin V1 Categories", type: :request do
  let(:user) { create(:user) }

  context "GET /categories" do
    let(:url) { "/admin/v1/categories" }
    let!(:categories) { create_list(:category, 5) }
    before { get url, headers: auth_header(user) }

    it "returns all Categories" do
      expect(json_body['categories']).to contain_exactly(*categories.as_json(only: %i[id name]))
    end

    it "should return success status" do
      expect(response).to have_http_status(:ok)
    end
  end

  context 'POST /categories' do
    let(:url) { "/admin/v1/categories" }

    context "valid params" do
      let(:category_params) { { category: attributes_for(:category) }.to_json }

      it "should add a new Category" do
        expect do          
          post url, headers: auth_header(user), params: category_params
        end.to change(Category, :count).by(1)
      end

      it "should return the last added Category" do
        post url, headers: auth_header(user), params: category_params
        expect_category = Category.last.as_json(only: %i[id name])
        expect(json_body['category']).to eq expect_category
      end

      it "should return success status" do
        post url, headers: auth_header(user), params: category_params
        expect(response).to have_http_status(:ok)
      end
    end

    context "invalid params" do
      let(:category_invalid_params) do
        { category: attributes_for(:category, name: nil) }.to_json
      end

      it "shouldn't add a new Category" do
        expect do
          post url, headers: auth_header(user), params: category_invalid_params
        end.to_not change(Category, :count)
      end

      it "should return error messages" do
        post url, headers: auth_header(user), params: category_invalid_params
        expect(json_body['errors']['fields']).to have_key('name')
      end

      it "should return unprocessable_entity - status code 422" do
        post url, headers: auth_header(user), params: category_invalid_params
        expect(body_json['errors']['fields']).to have_key('name')
      end
    end
  end
end